Detection of rainbow trout antibodies against viral haemorrhagic septicaemia virus (VHSV) by neutralisation test is highly dependent on the virus isolate used

1 Section of Fish Diseases, Division of Poultry, Fish and Fur Animals, National Veterinary Institute, Technical University of Denmark2 Division of Poultry, Fish and Fur Animals, National Veterinary Institute, Technical University of Denmark3 National Veterinary Institute, Technical University of Denmark4 unknown

DOI:

10.3354/dao074151

Abstract:

Three serological tests, enzyme linked immunosorbent assay (ELISA), 50 % plaque neutralisation test (50%PNT) and Western blotting (WB), were used to detect antibodies against viral haemorrhagic septicaerma virus (VHSV) in 50 rainbow trout broodstock from a rainbow trout farm endemically infected with VHS but with no clinical signs of infection. When the sera were examined by 50%PNT using the VHSV reference isolate DK-F1 or the heat attenuated DK-F25 mutant strain, no neutralizing antibodies were found. In contrast, when one of the virus isolates from the farm (homologous virus) was used in the 50 %PNT, 90 % of the fish were found to be positive. By examining a panel of different VHSV isolates in 50 %PNT, it was demonstrated that the virus isolate used as test antigen could significantly affect the sensitivity and titre determination in 50 %PNT for detection of rainbow trout antibodies against VHSV. When the sera were examined for the presence of VHSV antibodies by ELISA or WB, 61 % were found to be positive. When conducting WB analysis, the viral glycoprotein was the protein most frequently recognized, followed by the viral nucleoprotein.